This invention relates to a process for producing a heat-sensitive recording material having a coating structure excellent in smoothness, uniformity and stability, and also having excellent applicability to recording machines such as a facsimile machine.
A heat-sensitive recording material comprising a support and formed thereon a color developing layer comprising a color former and a color developer which develops a color by the reaction with the color former when heated is not so expensive, so that it is widely used as a recording medium in recording machines such as facsimile machines, printers, which are now compact and easy for maintenance. Recently, with miniaturization and high speed recording of facsimile machines, there is demanded a heat-sensitive recording material which is possible to conduct high speed recording with low energy.
In order to meet such a demand, it is proposed a heat-sensitive recording material comprising a base sheet and formed thereon a color developing layer having a surface roughness of an Ra smaller than 1.2 microns and a gloss smaller than 25% (U.S. Pat. No. 4,414,259). According to this U.S. patent, the color developing layer is formed on the base sheet by the blade coating technique, more concretely by using a bend type (generally called "bent type") blade coater. According to the blade coating method, there is an advantage in that a coating solution with a higher concentration to some extent can be used, but there is an disadvantage in that there are formed so-called streaks (scratching lines) due to high shear strength of a blade of a blade coater. Particularly, when the bent blade coater is used, it is necessary to use a low concentration solution in order to prevent streaks. When the low concentration solution is used, drying load increases and there easily bring about heat fogging and pressure fogging.
As to recording machine applicability, in order to enhance adhesion between a thermal head and a heat-sensitive recording material surface, the surface of the color developing layer is generally subjected to a smoothing treatment using a calender such as a super calender, gloss calender, and the like. But even if the surface of the color developing layer is simply enhanced in smoothness by the treatment using a super calender, or the like, it becomes impossible to obtain satisfactory dynamic sensitivity and further texture fogging and undesirable sticking are produced due to the pressure of calender.